1. Field of the Invention
The present invention relates generally to the field of semiconductor manufacturing. More specifically, the present invention relates to a method of depositing a film on a substrate in a high temperature chemical vapor deposition reactor so as to reduce pitting of a coated heater and thereby protect the heater from a corrosive environment.
2. Description of the Related Art
Chemical vapor deposition (CVD) is a well known process used in the semiconductor industry for applying a thin layer or film of material to a substrate, typically a semiconductor wafer, by introduction of reactant gasses in the presence of applied heat. Typically, CVD processes are conducted at elevated temperatures to accelerate the chemical reaction and produce high quality layers or films.
High temperature CVD reactors often rely on heaters to heat the silicon wafers for deposition of metal or dielectric films. The wafer is typically held on a flat susceptor or other heater element. In conventional CVD systems, aluminum heaters are commonly used. When used for depositing a film such as titanium, aluminum heaters may experience some limitations such as aluminum corrosion, temperature limitations, unwanted deposition, and manufacturing inefficiency. The aluminum corrosion caused by chlorine atoms and ions that are released into the process chamber when the titanium film is formed not only damages the heater, but may also lead to processing degradation issues relating to metal contamination in the devices and particulate generation.
Besides being susceptible to corrosion from chlorine, an aluminum heater is generally limited to operating temperatures less than about 480xc2x0 C. At temperatures greater than about 480xc2x0 C., aluminum heaters experience softening, possibly resulting from damage to the heater. Additionally, chemical species, such as chlorine, may more aggressively attack and corrode aluminum heaters at higher temperatures than at lower temperatures, thereby reducing the operational lifetime of the heater and undesirably requiring more frequent heater replacement. Heater replacement is expensive not only because of the cost of the heater, but also because the productive use of the deposition chamber is lost for the time the heater is being replaced.
In order to solve the above-mentioned problems, ceramic heaters or susceptors made of glass carbon or graphite coated with aluminum nitride (AlN) have been proposed as an alternative to using aluminum heaters in some applications. Fabricating ceramic heaters and using them in deposition processes, however, introduces several challenges.
Ceramic heaters typically have an electric heating element within a ceramic heater body, made of materials such as alumina (Al.sub.2 O.sub.3) or aluminum nitride, which protects the heating element from the corrosive environment of the deposition chamber while transmitting heat from the heating element to the substrate. Typically harder and more brittle than metals, ceramic materials may be difficult to machine, thereby requiring a simple mechanical design. Being somewhat brittle, ceramic may crack from thermal shock if repeatedly subjected to a sufficient thermal gradient. Cracking may also arise from the differential thermal expansion at the transition from the ceramic heater assembly to a material with a different thermal expansion coefficient.
Therefore, conventional heaters (for example, aluminum or ceramic) possess certain limitations for high temperature CVD processes. The prior art is deficient in the lack of effective means of depositing a film on a substrate in a high temperature CVD reactor. Additionally, the prior art is deficient in the lack of effective means of reducing pitting of coated heaters and protecting the heaters from the corrosive environment in the process chamber. The present invention fulfills these long-standing needs and desires in the art.
In one aspect, there is provided a method of depositing a film on a substrate in a high temperature chemical vapor deposition reactor, comprising the steps of polishing sharp corner(s) of the surface of a heater that provides heat to the substrate for deposition; coating the polished heater surface with a coating material; and depositing a film on the substrate in the CVD reactor, wherein the substrate is heated through the coated polished heater.
In another aspect, there is provided a method of protecting a heater from a corrosive environment in a chemical vapor deposition reactor, comprising the steps of polishing sharp corner(s) of the surface of the heater; and coating the polished heater surface with a coating material, thereby protecting the heater from corrosive environment in a chemical vapor deposition reactor.
In still another aspect, there is provided a method of reducing pitting of a coated heater in a chemical vapor deposition reactor, comprising the steps of polishing sharp corner(s) of the surface of the heater; and coating the polished heater surface with a coating material, wherein the resulting coated heater has a surface with reduced pitting compared to a coated non-polished heater surface.
Other and further aspects, features, and advantages of the present invention will be apparent from the following description of the embodiments of the invention given for the purpose of disclosure.